[PATCH][v2] PR rtl-optimization/119046: Don't mark PARALLEL RTXes with floating-point mode as trapping

[Kyrylo Tkachov]

Hi all,

In this testcase late-combine was failing to merge:
dup v31.4s, v31.s[3]
fmla v30.4s, v31.4s, v29.4s
into the lane-wise fmla form.
This is because late-combine checks may_trap_p under the hood on the dup insn.
This ended up returning true for the insn:
(set (reg:V4SF 152 [ _32 ])
        (vec_duplicate:V4SF (vec_select:SF (reg:V4SF 111 [ rhs_panel.8_31 ])
                (parallel:V4SF [
                        (const_int 3 [0x3])]))))

Although mem_trap_p correctly reasoned that vec_duplicate and vec_select of
floating-point modes can't trap, it assumed that the V4SF parallel can trap.
The correct behaviour is to recurse into vector inside the PARALLEL and check
the sub-expression. This patch adjusts may_trap_p_1 to do just that.
With this check the above insn is not deemed to be trapping and is propagated
into the FMLA giving:
fmla vD.4s, vA.4s, vB.s[3]

Bootstrapped and tested on aarch64-none-linux-gnu.
Apparently this also fixes a regression in
gcc.target/aarch64/vmul_element_cost.c that I observed.

Signed-off-by: Kyrylo Tkachov <ktkac...@nvidia.com>

gcc/

        PR rtl-optimization/119046
        * rtlanal.cc (may_trap_p_1): Don't mark FP-mode PARALLELs as trapping.

gcc/testsuite/

        PR rtl-optimization/119046
        * gcc.target/aarch64/pr119046.c: New test.

v2_0001-PR-rtl-optimization-119046-Don-t-mark-PARALLEL-RTXes.patch
Description: v2_0001-PR-rtl-optimization-119046-Don-t-mark-PARALLEL-RTXes.patch